The present invention relates to gantries for medical diagnostic equipment. It finds particular application in conjunction with nuclear or gamma camera systems and will be described with particular reference thereto. However, it is to be appreciated, that the invention will also find application in conjunction with PET and other diagnostic equipment.
Heretofore, nuclear or gamma cameras have included a detector head which receives radiation emanating from the patient. The head includes a flat scintillation crystal which converts incident radiation to flashes of light. Internal electronics convert each flash of light into an indication of the location and energy of the received incident radiation event. Collimators are commonly mounted to the face of the detector head such that the scintillation crystal only receives radiation coming generally straight toward it. Generally, the collimators are a series of lead vanes arranged in a grid. The height of the vanes and their spacing control the angle at which received radiation may differ from perpendicular. Different collimators are provided for different types of medical procedures.
Various mechanical gantry systems have been provided which enable the detector head, typically on the order of several hundred pounds, to be positioned at a selected location over the patient. Commonly, the gantry is also motor controlled such that the detector head can be moved continuously or intermittently either (i) longitudinally along the patient or (ii) circumferentially around the patient. Many gantry systems also support a second detector head which is positioned 180.degree. oppositely around the patient from the first head.
In one of the prior art gantry systems, each head was mounted on a pair of arms. The arms are centrally pivotally with a large diameter bearing ring and had a counterweight at the other end. Although the counterweights reduce the effective weight of the camera head the length of the cantilevered arms required that the gantry consume a relatively large area. Moreover, moving counterweights tended to be a safety hazard to operator personnel.
Another prior art camera mounted the head pivotally to a single arm with appropriate control mechanisms to move and rotate the arm and head. By eliminating the counterweights, space was saved. However, the large weight of the heads necessitated solid parts and strong drive mechanisms.
In another prior art system, the head was mounted for longitudinal movement along an elongated horizontal beam. The beam was connected at opposite ends for rotation around the circumference of the patient.
In another prior art system, the patient was received along an axis of a pair of spaced, parallel large diameter bearings. A camera head and a counterweight were connected oppositely with the bearings. Alternately, a second head was connected with the inner race diametrically opposite the first head.
For axial scans, the camera head and the patient were moved relative to each other. In some of the prior art systems, the entire camera gantry was mounted on floor rails to be moved longitudinally relative to a stationary patient.
Difficulties were encountered in the prior art gantry systems during changing of the collimators. Typically, the collimators were stored flat, such as on the top of a cart. The cart would be wheeled to a preselected location relative to the gantry. The head was positioned horizontally, facing down, typically about three feet off the floor. Either the cart top or the detector head were moved until the head and collimator were aligned for mounting. Typically, the carts had an adjustment mechanism for moving the collimator up and down. The detector head would be positioned at a preselected collimator mounting position, generally horizontally facing downward about three feet from the floor. The cart would then be positioned underneath the head and raised. The position of the cart would be adjusted as the collimator was raised to assure that bolt apertures in the collimator aligned with complementary bolt apertures in the detector head. This was a tedious alignment procedure. Bolts or other connectors were passed through apertures in the collimator and threadedly or otherwise connected to the head.
One problem with this type of collimator system was that an extended amount of floor space was required for collimator storage. Each stored collimator required an area its own size. With a dual head camera system, the collimator storage requirements were doubled.
Another problem with these prior art collimator systems is that bolting and unbolting collimators from the detector heads was time consuming and required special tools. Due to the heavy weight of the collimators, care had to be taken to tighten the bolts sufficiently but without damaging the soft lead collimator or detector head housing.
The lead collimators were typically a few hundred pounds. Collimators of different heights or different vane widths or spacings vary significantly in weight. The change in weight from collimator to collimator and the great weight of the detector head could alter the ability of the gantry to position the detector head properly. The weight tended to cause the head to sag or cart has the gantry rotated the head.
The present invention contemplates a new and improved gantry system which overcomes the above-referenced problems and others.